In closed circuit refrigerant expansion systems such as in an organic rankine cycle (ORC) system, lubrication of the moving parts of the turbine is necessary to ensure continuous and prolong periods of operation. For that purpose, the turbine is provided with an oil accumulator or sump that is intended to have a minimum level of oil contained therein at all times to provide an oil source for properly lubricating the turbine parts.
In such a system, it is recognized that a certain amount of the lubricating oil becomes entrained within the working fluid or refrigerant that is circulated throughout the system. In order that the oil is returned to the oil sump, an oil separator is commonly provided such that the oil entrained refrigerant passes through the separator, with the separated oil being returned to the sump and the separated refrigerant being passed back into the primary working fluid circuit.
From time to time, as part of normal and regular maintenance, it is necessary to change or add oil to the sump. It is possible that, when a technician checks the level of the oil in the sump, it appears to be low because substantial amounts of the oil may not have been returned to the sump from the remaining portion of the system due to a recent operating event such as a rapid shutdown. If the technician then adds oil to bring the level of the sump up to a level which he believes is acceptable, then, when the oil in the system is returned to the sump, it will raise the level to an unacceptably high level so as to exceed the safe operating level and come in direct contact with the bearings. This, in turn, may cause the bearings to “skid” and to fail.
What is needed is a method and apparatus for preventing a rise in the oil level of the sump to a level that presents a danger to the bearings.